1. Field of the Invention
Present invention relates to a method for preserving cooked foods and a vacuum sealed preservation container therefor and, more particularly, it relates to a method for preserving cooked foods and a vacuum sealed preservation container therefor for safely storing perishable foods and cooked foods such as heated-cooked foods cooked by heating, other than perishable foods, for a long period of time.
2. Description of Related Prior Art
Method for preserving heat-cooked foods has been disclosed, for example, in Japanese Patent No. 1649898 (Japanese Patent Publication Hei 3(1991)-8750).
Existent preservation containers include tupperware, tightware, and tightware with pressure control valves.
Tupperware has a lid made of a soft resin, which is a mere container not having any food preserving function since the container has no complete barrier property for external air.
Tightware has a constitution as shown in FIG. 6 and when heat-cooked foods are filled while hot and tightly closed by locking a securing tool, the pressure inside the container is reduced after cooling and a lid cannot be detached any more. Tightware with a pressure control valve is constituted, as shown in FIG. 7, such that a pressure control valve 11 (operating in a manner opposite to a check valve) is provided to a lid. When heat-cooked foods are filled while hot and external air is allowed to enter automatically even after cooling to prevent reduction of pressure in the container thereby making the lid removable. However, this also results in a possibility of invasion of bacteria, which is not preferred in view of food preservation.
Further, upon heating foods in a microwave oven, since stoppers have to be detached before heating in any case, this cannot be applied to the present invention. However, the preservation method as disclosed in Japanese Patent Publication Hei 3-8750 has a feature of filling cooked foods while hot sterilizing by microwave heating in a microwave oven and then preserving them in a tightly sealed state and the method is limited to filling while hot. That is, it is conditioned that foods are packed before cooling. Since heat-cooked foods are in a sterile state from the end of heating to a state cooled to approximately 60.degree. C. and, further, in a substantially sterile state till it is cooled to approximately 40.degree. C., and a worry of secondary contamination, if any, will be little. Therefore, it is apparent that foods can be preserved for a considerable period of time with no petrifaction when they are heat-sterilized in a microwave oven and stored in a tightly sealed state, and this method is used for single kinds of foods.
When the container is actually used, for example, as a lunch box, not only single kind of foods but also two or three kinds of heat-cooked foods, or those foods having difference in the time elapsed after the heat cooking are often packed in combination into the container. Further, if green vegetables as non-heated foods having high risk of contamination are contained as a portion thereof, it may prevail contamination to other heat-cooked foods.
Further, those foods such as hamburgers made from materials such as minced meat of low heat conductivity cannot be heated sufficiently to a central portion, so that pathogenic Escherichia coli. O157 may some time remain.
With another view point, food poisoning, food accident, etc. are often caused actually due to occurrence of secondary contamination by leaving foods at an ambient temperature after heat-cooking, particularly, depending on the duration of time of leaving in the summer season, inadequacy for the control of the state where the foods are left, and also caused from the container.
Further, in a state where bacteria present in the initial stage are killed by the heat cooking, since newly attached contaminating bacteria grow extremely rapidly, this may cause food poisoning or the like ("Practical Food Hygiene for Women", written by Hiroshi Nishida Published from Ohm Co. p 250-252, issued 1990).
Particularly, when the container is taken out in a normal temperature circumstance as a lunch box particularly in the summer season, it has to be exposed in a severe condition of 30.degree. C. to 35.degree. C. for at least 6 to 10 hours inevitably.